dependency-injection

Prevent hidden coupling in Python services by enforcing explicit constructor-based dependencies. This requires providing all collaborators as parameters during instantiation, avoiding hidden defaults or direct environment variable access inside the service logic.

Structuring dependency injection for unit testing involves passing required collaborators via the constructor at the composition root. This clear separation of concerns allows you to easily supply mocks and verify business logic independently.

Constructor-based dependency injection improves software architecture by enforcing a clear top-down configuration flow from entry points to implementations. It establishes a distinct boundary between initialization wiring and business logic, ensuring fail-fast behavior for missing dependencies.

Services should avoid reading environment variables directly to prevent hidden coupling and maintain testability. Explicit constructor parameters require configuration at the application entry point, ensuring services remain pure and fail-fast when collaborators are missing.

You can apply this pattern to existing Python codebases by refactoring services to accept required collaborators as explicit constructor parameters. Moving configuration to the composition root establishes clear top-down wiring without hidden defaults.